[vsnet-grb-info 18836] GRB 161218A: POLAR observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20287
SUBJECT: GRB 161218A: POLAR observation
DATE:    16/12/18 18:58:48 GMT
FROM:    Zhengheng Li at POLAR  <lizhengheng at ihep.ac.cn>

Z. H. Li (IHEP), Y. H. Wang (IHEP), S. L. Xiong (IHEP) 
report for the POLAR collaboration:

At 2016-12-18T03:47:34.634 UT (T0), during a routine on-ground 
search of data, POLAR detected the GRB 161218A, 
which was also detected by the Swift/BAT (trigger #727288).

The POLAR light curve consists of a single peak,
with a duration (T90) of 6.76 s measured from T0+0.25 s .
The 0.25s peak rate measured from T0+1.25 s is 2660 cnts/s,
The total counts is about 6644 cnts.  The above measurements are
in the energy range of about 80-500 keV.

The preliminary estimation of minimum detectable polarization (MDP) 
is 32.5%[3-sigma, statistical only]. Follow-up observations are 
strongly encouraged.

LC_URL:
http://polar.ihep.ac.cn/grb/2016/GRB161218A/lc/POLAR_lc_grb161218158.png

Using the best location from the Fermi/GBM, which is (J2000):
RA:    245.257     [deg]
Dec:    -4.114     [deg]
Err:     3.00      [arcmin]

the incident angle in POLAR coordinate at T0 is:
theta:  24.327  [deg]
phi:   356.614  [deg]

The analysis results presented above are preliminary.

POLAR is a dedicated Gamma-Ray Burst polarimeter (50-500 keV) on-board 
the Chinese space laboratory Tiangong-2 launched on Sep 15, 2016. More 
information about POLAR can be found at http://polar.ihep.ac.cn/en/ , 
http://isdc.unige.ch/polar/ and http://polar.psi.ch/html/ .